The heart is a four-chambered organ located in the thoracic space. The heart is responsible for pumping blood through the body, through two distinct circuits. One circuit takes blood low in oxygen from the systemic venous system, which collects in the right atrium (one chamber). The atrium pumps the blood into the immediately lower chamber, the right ventricle. In passing from the atrial chamber to the ventricular chamber, the blood passes through the “tricuspid” valve opening, so named because of the three leaflets (cusps) of the valve. The right ventricle contracts to pump the blood into the lungs (second circuit) and in so contracting, forces the tricuspid valve leaflets closed, thus preventing backflow of blood into the right atrium.
The oxygenated blood flowing back to the heart from the lungs enters the left atrium (third chamber) and collects there until the atrium contracts and pumps the blood through the mitral valve into the immediately lower chamber, the left ventricle, during diastole. When the left ventricle contracts to pump the blood into the systemic circulation (back to the first circuit) during systole, the mitral valve leaflets are closed, preventing backflow of blood into the left atrium and the pulmonary circulation. The mitral valve is comprised of two valve leaflets. The atria contract simultaneously, as do the ventricles.
Another set of valves is present in the main artery of the left ventricle, the aorta and the main artery of the right ventricle, the pulmonary artery. These valves are called the aortic and pulmonary valves, respectively and they are similar in appearance.
The anatomy of the mitral and tricuspid valves is similar, but quite distinctly different from the anatomy of the aortic and pulmonary valves. These valves are comprised of the following six different components: the left (or right) atrial wall, the left (or right) ventricular wall, the annulus, the leaflets, the chordae tendinae and the papillary muscles. The annulus is a zone of junction that serves as the attachment of the muscular fibers of the atrium and the ventricle and as the attachment of the mitral (or tricuspid) valve. Annular tissue is pliable permitting contraction of the annular ring when the ventricles contract and thus narrowing the aperture.
The annulus forms the foundation for the leaflets, which are secured to the ventricular wall by way of the chordae tendinae, thin fibrous cords attaching the free edges of the leaflets to the papillary muscles, which are elevations or extensions of the ventricular wall. All structures are covered by endothelial cell lining but the contractile elements (muscles) of the atria and ventricles are capable of independent movement. The other structures are largely fibrous in nature, composed of dense fibrous connective tissue and collagen.
When the ventricles contract during systole, the pressure within the ventricles forces the leaflets upward until the free edges contact. This is called coaptation. The free edges of the leaflets are inhibited by the chordae tendinae from prolapsing beyond the plane of the annulus and into the atrial chambers. When the normal mitral or tricuspid valves close, the valve becomes competent and no blood escapes through the annulus. The operation of these valves (plus the normal closure of the aortic and pulmonary valves) ensures that the heart functions as a one-way pump.
As one understands the complex operation of the mitral or tricuspid valves, one can begin to appreciate the number of possible causes for failure of proper function of these valves. Some of these are: loss of pliability of the annulus leading to decreased contractibility; widening of the annulus; thickening, shortening or swelling of the leaflets; dilation of the ventricle; elongation or breaking of the chordae tendinae; and elongation of the attachment of the chordae tendinae with the papillary muscles or ventricular wall.
Individual or combinations of these causes for failure eventually lead to loss of coaptation of the leaflets, loss of competence of the valve and decreased efficiency of the heart as a one-way pumping mechanism. When the latter occurs, various symptoms are seen in the patients, including breathlessness or lack of stamina and heart murmurs.
Repair of the incompetent valves is designed to address two functional conditions of the leaflets, either the opening or closing of the leaflets is increased or restricted. The former condition, called leaflet prolapse, exists when the free edge of one leaflet overrides the annulus when the ventricles contract. The latter condition occurs when the restricted leaflet motion prevents the leaflets from opening. The other possible functional condition is where the valve leaflets may be functionally normal, but the annulus does not contract or is too enlarged. When this occurs the leaflets will not close effectively.
The current accepted modes of treatment of these conditions described for the mitral and tricuspid valves include the following: valvuloplasty, in which the affected leaflets are remodeled to perform normally; repair of the chordae tendinae and/or papillary muscle attachments; and surgical insertion of an “annuloplasty” ring. This requires suturing a flexible support ring over the annulus and tucking the annulus to constrict the radial dimension.
Each of these procedures requires open-heart surgery and cardiopulmonary bypass procedure, in which the heart is removed from the blood circuits as the circuits have been described above and a pumping system circulates the blood through the patient during the surgical procedure. The heartbeat is stopped and the heart is usually cooled and infused with a cold nutrient solution during the procedure. Open-heart surgery with cardiopulmonary bypass is a very expensive procedure, requiring considerable time, multiple surgeons and a host of assisting personnel to operate the equipment, monitor the patient and proceed with caution but quickly for the patient's benefit. These procedures are also associated with serious risks, including death and adverse events for the patient and the patient has a long painful course of recovery, first in the hospital, then at home.
Oz et al. in U.S. Pat. No. 6,269,819 discloses an apparatus for repairing valve leaflets comprising a grasper capable of grabbing and co-apting the leaflets of valve to cure mitral regurgitation. The principles of the “grasper” arrangement and its mechanism as disclosed are incorporated herein by reference. Oz et al. does not disclose a medical system having a fastening applicator that comprises a pair of grasping-electrodcs means adapted for holding and engaging portions of opposing heart valve leaflets together and for applying suitable energy to fasten the portions.
Robertson et al. in U.S. Pat. No. 6,203,553 discloses a surgical stapler for securing a prosthetic heart valve within a patient by driving a first leg of the stapler assembly through a peripheral cuff of the prosthetic heart valve and crimping a second leg of the stapler assembly in a direction toward the first leg such that the second leg pierces a portion of heart tissue surrounding the prosthetic valve for securing purposes. The principles of “stapler” arrangement and its securing mechanism as disclosed are incorporated herein by reference. Robertson et al. does not disclose a medical system having a fastening applicator that comprises a pair of grasping-electrodes means adapted for holding and engaging portions of opposing heart valve leaflets together and for applying suitable energy to fasten the portions.
This invention discloses a series of devices to be used to repair leaking valves with normal leaflets (that is, abnormal annulus) or leaflet prolapse, without the disadvantages associated with open-heart surgery, because the device is inserted into the heart via the blood vessels, through the skin in the groin or neck area percutaneously. During the procedure, the patient may be awake, sedated or anesthetized and the device and progress of the procedures are monitored and guided using fluoroscopy and echocardiography, both noninvasive methods, in the continuously beating heart. Obviously fewer personnel are required to assist with the procedure. When the procedure is completed the patient may be discharged within hours to days. All of these contrasting features to open-heart procedures make the use of the stapling device a potentially valuable resource for the interventional cardiologist. These specialists will be able to add yet another “minimally invasive” procedure for treatment of their patients.